1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to accurate signal detection by wireless communication devices operating in such wireless communication systems.
2. Description of Related Art
In a wireless communication system, wireless communication devices are constantly listening to one or more wireless communication resources (e.g., radio frequency (RF) channels) to determine whether they are intended recipients of a wireless communication. In a wireless local area network (WLAN) as defined by standards, such as IEEE802.11a, b, g, Bluetooth, et cetera, wireless communication devices monitor RF frequencies for a prescribed preamble. Typically, when the wireless communication devices are in the monitoring mode (i.e., seeking the preamble), they are in a limited operational state to reduce power consumption. When the prescribed preamble is detected, the wireless communication device becomes fully operational and thus is consuming more power.
To detect a valid IEEE802.11a or g preamble, wireless communication devices employ an auto correlation function to compare receive signals (i.e., received RF signals down-converted to baseband signals) with a delayed representation of the received signals. As is known, an IEEE802.11 wireless communications are packet-based where each packet includes a preamble and data. The preamble includes a plurality of repetitive short training sequences (STS) followed by a guard interval (GI), which is followed by a plurality of long training sequences (LTS). If valid short training sequences (STS) are being received, the auto correlation circuit is effectively comparing one STS to another to determine the validity of STS being received. If the auto correlation indicates that a valid STS series is being received, it continues the validation process by performing an auto-correlation on the long training sequences (LTS). If the received signal passes both STS and LTS auto correlations, then the signal is deemed to be valid.
While such auto correlation works to detect valid signals, it sometimes falsely detects interfering signals or adjacent channel signals as valid signals. When this occurs, the wireless communication device is fully activated and thus consumes power unnecessarily. In addition, such false positive detections limits data throughput of the wireless communication device since it is processing invalid data.
Therefore, a need exists for a method and apparatus that accurately detects the presence of valid signals.